Transition of triazole-resistant Aspergillus fumigatus isolates in a Japanese tertiary hospital and subsequent genetic analysis

Abstract Objective To evaluate the annual variation in the frequency of patient-acquired azole-resistant Aspergillus fumigatus (ARAf), and correlate it to the amount of oral triazole prescribed, in Nagasaki, Japan. Methods A. fumigatus isolates from respiratory specimens collected in the Nagasaki University Hospital (NUH) between 1996 and 2017 were included in the study. The amount of oral triazole prescribed in NUH since 2001 was obtained from the medical ordering system. Mutations in cyp51A, hmg1, and erg6 genes of ARAf were also analysed. Results From a total of 240 ARAf strains, 12 (5%), 6 (2.5%), 15 (6.25%), and 3 (1.25%) strains were resistant to itraconazole (ITC), voriconazole (VRC), to either ITC or VRC, and both triazoles, respectively. The amount of prescribed VRC increased annually, and was three times as large as that of ITC in 2017. All eleven patients harbouring ITC-resistant strains had a history of prior ITC treatment, while only one of six patients harbouring VRC-resistant strains had a history of prior VRC treatment. cyp51A mutations were recorded in 10 strains; however, tandem repeat mutations of the promoter region of cyp51A were not observed. Several azole-resistant strains had non-cyp51A mutations. Conclusions The frequency of patient-acquired ARAf is not increasing in Nagasaki, Japan. Furthermore, the prevalence of VRC-induced ARAf was rare despite the remarkable increase in the amount of prescribed VRC. Mutations in genes other than cyp51A should also be considered when ARAf strains are obtained from patients treated with azole antifungals.